Hydraulic steering motor and shimmy dampener



March 18, 1952 H, CHxsHoLM, JR., ET AL 2,589,341

HYDRAULIC STEERING MOTOR AND SHIMMY DAMPNER Filed Sept. 6, 1946 4 Sheets-Shee' l Bernard/Mnner bgZ/MMM @22,5

March 18, 1952 H. l.. Hlsl-loLM, JR., ET AL 2,589,341

HYDRAULIC STEERING MOTOR AND SHIMMY DAMPNER Filed Sept. 6, 1946 4 Sheets-Sheet 2 March 18, 1952 H. 1 cHlsHoLM, JR., ET A1. 2,589,341

HYDRAULIC STEERING MOTOR AND SHIMMY DAMPNER Filed Sept. 6, 1946 4 Sheets-Sheet 3 b g w A George Farrell (6 BernaraEOConno March 18, 1952 cHlsHoLM, JR., Erm. 2,589,341

HYDRAULIC STEERING MOTOR AND SHIMMY DAMPNER Filed Sept. 6, 1946 4 Sheets-Sheet 4 Vm.- I

Patented Mar'. 18, 1952 HYDRAULIC STEERING MOTOR AND SHIMMY DAMPENER Harry L. Chisholm, Jr., v.George Farrell, and Bernard E. OConnor, Buffalo, N. Y., assignors to Houdaille-Hershey Corporation, Detroit,

Mich., a corporation of Michigan Application September 6, 1946, Serial No. 695,112

This invention lrelates to an improved device especially suitable for steering and shimmy con- 16 Claims. (c1. ici-41) trol of thesteering wheels of airplane landing issued April 3, 1945, and 2,383,773, issued August In the use of a steering motor and shimmy dampener of this type in an airplane, forexample, a vaned piston is operable in hydraulic Working chambers and is connected with the wheel to be steered and controlled. A control valve structure operable from the pilots seat in the associated airplane controls the direction of flow of hydraulic fluid under pressure to the piston vanes in said working chambers to rotate the piston and thereby turn the steering wheel in the desired direction. Appropriate connections are afforded with a source of hydraulic pressure fluid also under control from the pilots seatfin the airplane, and with a discharge line for carrying oif spent pressure fluid.

When the pressure fiuid is shut off, the device automatically functions as a shimmy` damper, inter-conecting piston supported control'fvalve structure cooperating to check the fiow of hydraulic fluid between the working chambers to dampen shimmy of the associated wheel.` .In this connection, it may be stated, that the device operates as a filled hydraulic system, andsafety check valve means function, whenever the hydraulic pressure fluid supply is cut off or the pressure drops below operating value for steering, thus maintaining thedevice filled with ,the hydraulic fluid for eicient operation as a shimmyY dampener.

An important object of the invention is to provide in a hydraulic steering motor and shimmy dampener of the kind indicated positive sealing and substantially wear-free main` control valve means.

Another object of the invention is to provide novel poppet valve control mechanism which is particularly suitable for controlling the direction of hydraulic pressure uid flow in a hydraulic steering motor device. Y

Still another object of the invention is to provide a hydraulic steering motor control valve mechanism having an unusualy high safety factor and positive operating characteristics.

A further object of the invention isto provide in a hydraulic steering motor for steering wheels operating means enabling Visual indication of the steering position of the wheel. L

Another object of the invention is to provide in an improved hydraulic steering motor and shimmy dampener advantageous means for effecting replenishment of the hydraulic fluid in 'order to'maintain a filled system within the de vice.

It is also an object ofthe invention to afford improved means for venting air from rthe hydraulic system of a hydraulic steering motor and shimmy dampener. l

A still further object of the invention is to provide simple and effective thermal pressure relief for hydraulic steering motor and shimmydampener.

Yet another object of the invention is to provide a hydraulic steering motor and shimmy dampener structure in which certain parts of relatively small mass subject to relativelyhigh hydraulic pressures are appropriately relieved from excessive deflection 'dueto the hydraulic pressures.

A still further object of the invention is to provide a novel steering motor and shimmy dampener which is readily adaptable in construction to meet various requirements as to function and available working space and which is especially suitable for highly pressure sensitive operation.

These and other objects, features and advantages of the present invention will be readily apparent from the following detailed description of certain preferred embodiments of the invention, taken together with the accompanying four sheets of drawings, wherein: Figure l is a vertical sectional view, more or less conventionalized, through a hydraulic steering motor and shimmy dampener unit embodying the vfeatures of the present invention;

Figure V2 is a fragmentary vertical sectional View taken in substantially the same plane as Figure 1 but showing various parts in respective positions thereof assumed during operation of the unit as a steering motor;

Y' Figure 3 is a fragmentary, enlarged sectional view taken substantially along the line of III-III of Figure 1;

Figure 4 is a slightly enlarged, fragmentary vertical sectional detail view taken substantially along the line IV-IV of Figure l;

Figures- 5, 6, 7 and 8 are transverse sectional detail views taken substantially along the lines V-V, VI-VI, VII-VII and VIII-VIILrespec.- tively, o f Eigurerl;

Figure 9 is a fragmentary, vertical, sectional detail view showing a modified form of poppetvalve structure;

Figure 10 is a transverse, sectional, detail vi'ew taken substantially along the line X-X of Figf Figure 11 is a fragmentary, ,verticahsectional ure l;

view showing a modified form. of replenishing valve structure; and

Figure 12 is a fragmentary, longitudinal, sec.-

tional view taken in substantially they samel plane as Figure 1 but showing modified structuren for? l*are preferably identical in structure and disposed on diametrically opposite sides to fit relatively ,snugly against the internal wall of the cylinder I5 and to cooperate in relatively slidable relay divided by longitudinal and diametrical integral duits, control shafting, etc., have been omitted in the vpresent instance since they are well known. If more detailed information relative thereto isV desired, reference may conveniently be had Y a series of longitudinal serrations 24 for interlocking, attachment thereto of operating, lever structure for connection with the wheel to be steered;-

Asshown, the lower closure. flangev 22' is of relatively.v massive structure and thoroughly capable of withstanding substantial hydraulic pressure withoutV deflection.Y For convenience the outer end thereof is of generally conicallyf'taperedshape in .order to accommodate a securing ringjnut25 'threadedintothe .end of the cylinder I5janddrivinggtoward the contiguous'margin o f the closure'flange'22 lwhereby to clamp the latter-v against tlieshoulderv 23 and'at the sametime compress packing 21 to afford a'fluid'tight'joint'.

Asubstantially fluid tightjoint between the rotary piston shaft 2I andthe'internal bearing wall'of the closureflange22 is'faiforded by' packing 28 compressed bya ringnut 29 encircling .the shaft 2J and threaded `into an annular recess or rabb'etgroove 30 at the outer end of the .bearingwall.,

The closure flange.member22 carries. apair of. integral longitudinally. inwardly extending stationary vanes or abutment members 3 I. These vanes 34 extending radially from the piston 20. Keys,35.lock;1the abutments 3| to the cylinder -I5.". Packing or sealing strips 31 aord a wiping liquid seal .between the abutments and the piston 20'. Sealingonp-acking strips 38 provide a wiping liquicLseal between each of the vanes 34 and the wall v of. the cylinder;

A closure for the opposite or upper end of thecylinder-I5 is afforded by a flange or closure plateel 39.. In the present instance, the closure plate flange 39 is preferably a relatively thin platewhich supports a head structure 40 and is received"v againstan annular outwardly 'or' upwardly facinginternal shoulder 40a formed in the .internalcylinder wall I5 inpreferably a plane withthe.adjac'ent ends of the abutments 3I and theA end" of the piston 20. Securing the closure memben39 and the head 40 in place is a ringnut 4Iithreaded into. the'upper end of the cylinder I5l.and"driving: against a lateral ange 42 on the head' whereby "to clamp the flange 42 and the -margin of ithe closure` member 39 against the shoulder 40a. PackingAB compressed-by the ring nut 4I affords'a liquid tight joint between the.

closuremembers 22 and 39, respectively, are af.

fordediby packing'or sealing strips 45 and fitted into'. the vane'. ends.

According to thepresent invention, means are 'provided' for thecontrolled admission of hyldraulic fluid selectively'to the working chambers 32 and'33 to drive the piston vanes 34'foreffecting rotary steering movement of the piston 20. Hydraulic pressurev fluid isadapted to be delivered'from any'suitable'source under the requisite pressure'into an'inlet41`provided in the head 4B.

From"the"inlet, the pressure fluidV passes through agverticalpassage' and-past a spring-biased disk-type check yalve 49'into a lateral Iconductingjpiassagef'SO formedV in theouter face ofthe closure*v plate- 39. Thence, the pressure fluid passes'into anannular distribution channel 5I also'formed'in the outer'face of the closure plate 39, surrounding a cylindrical control valve plug 52 extending in slidable bearing relation axially through the closureplate.

It may be noted that since the closure plate 39'isfsubjected' to substantially equal hydraulic pressure 'on'."both' sides `while acting as a steering motori a' virtually balanced pressure condition prevails and frees it of'forces that might tend to deflect the plateaxially. Hence, the plate can b'e lmade fairly, thin vandthusconserves space in the assembly.v

The `control. valve. plug 52S is ofjelongated cylindrical form and the inneror lower portionis secured fast within an axial boreY 53 provided therefor in the upper end of the piston 28. The outer or upper portion of the plug extends upwardly in sliding, bearing relation into a bore 54 in the head 4D. Rigid assembled relation of the control valve plug 52 and the piston 29 is effected by means of screws 55 extending longitudinally through the plug into vthe piston.

Pressure iiuid communication between the annular distribution channel 5I and the working chambersV 32 and 33 is afforded by a system of bores, passages and ports in the valve plug 52 and the piston 29. For this purpose, a radial port 51 (Fig. 7) opens inwardly from the chan- 'iiel' 5| into the valve plug 52 and communicates with a vertical bore 58 affording a passage communicating with a lateral delivery port 59 (Fig. 8) which opens adjacent the top of the piston 20 and closely adjacent to one side of the vane 34 within the working chamber 32. Another radial port 69 opens inwardly into the plug 52 and affords communication between the distribution channel 5| and the working chamber 33 by way of a vertical bore 6I affording a passage communicating with a lateral delivery port B2. 'Ihe latter opens into the working chamber 33 at the top of the piston 20 closely adjacent to the vane 34 therein and on the same side of such vane as the port 59 with respect to its ccmpanion vane 34. Thus, it will be apparent from Figure 8,`thatl hydraulic pressure iiuid entering the working chamber 32 by Way ofthe delivery port 59 will work between the opposing faces of the confining abutment 3| and the vane 34 to drive the piston 20 counterclockwise as viewed. On the other hand, the pressure fluid delivered through the port 62 into the working chamber 33 will act to drive the piston 29 clockwise.

In order to admit the hydraulic pressure fluid selectively to either of the working chambers 32 or 33 for steering purposes, the pressure fluid passages and 5| are provided with control valves 63 and 64, respectively. By preference, these are poppet valves which are adapted to be operated by the pilot of the airplane with which the device is associated. To this end, the poppet valves 63 and 64 are disposed in spaced relation in a straight line on a Ichord of the valve plug 52 and each is preferably urged upwardly against a respective seat 65 located intermediate the inlet and delivery ports of its pressure fluid bore by a coiled expansion spring 61 of stronger bias than the maximum opposing line pressure of the hydraulic fluid.

'Each of the poppet Valve members 93 and 64 is provided with a base or stem 68 of reduced diameter extending past the respective delivery ports 59 and 62 and terminating in a cylindrical basev 69 of enlarged diameter and formed with an upwardly directed pressure face 10 opposing a downward pressure face 1| on the valve member and of equal area. A bottom facie 12 on the base 69 is abutted by the upper end of the cooperating expansion spring 61. Affording a close sliding fit with the base 69 is a cylindrical guide'sleeve 13 providing a lower reduced diameter axial bore 14 serving as a loose guide fluid tight seal between the bearing surfaces of the b'ase member and the bearing sleeve 13. assure a fluid tight joint between the bearing sleeve 13 and the wall of the lower enlarged por- 6 -tion of the bore 58 or 6|, respectively, packing material is preferably .disposedbetween the interfaces thereof, as indicated at 18. 1

Each of the poppet valves 63 and 64 is provided with a cylindrical actuating head 19 at the upper end of an integral .reduced diameter stem 80. The head 19 is of a diameter to t in relatively close sliding bearing relation within an upper extension of the respective :pressure fluid bore in Which it is housed. A ring packing 8| in an intermediate annular groove 82 encircling. each of the heads 19 affordsa substantially leak-proof fluid seal. 'Ihe head 19 has alower face 83 which is preferably of substantially the same exposed area as the area of the opposing respective valves 63 and B4, and substantially the same area as the upper face 19 ofthe base 69. An upper face 84 on the head 19 is preferably of substantially the same area as the lower face 12 `of the base 69 of the poppet valve structure. l

Acting against the respective upper faces 84 of the poppet valve heads 19 and adapted to urge the pressure fluid controlling poppet valves 63 and 64 selectively slidably'axially in opposition to the bias of their respective springs 61 are actuating means comprising, in the present instance, a rocker plate 85 (Figs. 1, 4 and 5)'. This plate 85 overlies the poppet valve heads and is rotatably mounted on a horizontal diametrical axis midway between the poppet valves B3 and 64 by means of pins 81 extending radially from trunnions 88 and journaled in an upstanding annular ange 89 at the upper end of the valve plug 52. This iiange 89 projects into a housing chamber 98 in the upper end of the head 40. The axis of the rocker plate 85 extends between the axes of the poppet valves 63 and 64 so that when the rocker plate is rocked toward the poppet Valve 63 an axially adjustable abutment screw 9| will act upon the head lface 84 of such valve and depress the valve to unseat it. Tilting of the rocker plate in the opposite direction causes an adjustable abutment screw 92 carried thereby to engage and depress the head 19 of the valve 34. Adjustment of the abutment screws 9| and 92 will properly compensate for any inaccuracy or lack of uniformityv that vmay show up in the actuating relationship of the rocker plate to the poppet Valves after completion of the poppet Valve assembly. v'

For actuation thereof, the rocker plate 85 includes means such as an integral tilting ball or knob 93 carried by an upstanding rocker arm 94 and disposed directly over the rockeraxis of the plate. For actuating the rocker arm ball 93 means such as a reciprocable and oscillatable fork 95 engages the same and is carried by or integral with a rotatable and reciprocable plunger 91 projecting slidably in an axial bore 91a in the valve plug 52 (Figs. 1 and 6). In the present instance, the upper end of the plunger 91 which carries the fork 95 is formed as an enlarged head 98 which extends, downwardly through a central clearance aperture 99 in the rocker plate. The fork 9.5 is formed fiat, at least on its under face, to lie on top of the rocker plate and retain it in a neutral horizontal position as shown in the broken outline position in Figure 4. The fork 95 is formed with parallel sides to be received within a locking slot |00 formed for this purpose in the upstanding marginal flange 89 of the valve plug. While thefork 95 is held in the locking slot |09 it cannot be oscillated and thereby serves to lock the rocker plate in neutral position.

7 .Abovethe .baseof the lockingrslot |00, a distance somewhat .less than .the thickness ofthe lfork 95, the slot widens outin the form of oblique cam-surfaces li at therespective-.opposite,sides of this slot yto a predetermined vwidth defined ,by vertical v.limit edges |02 which deiine the range of oscillationof the fork .in l.swinging therocker arm'ball 93,.thereby.rocking Atheplate 35. Y.

" .By preference the forkcarrying plunger- Sl .is pos'rtivelyiurged .axially downwardly to maintain thezrockmg fork 95 .normally in the rocking- 'plate .locking position within the slot |00, .and

means are .provided .for unlocking the fork lS5 Vbyzraisingthe plunger 31 through admission of rthe .hydraulic pressure .fluid .to the unit .when

steering action thereof is to be eiected. Forthis purpose, `a coiled expansion spring |03 isseated within an axial spring pocket bore |04 within .the plunger 91 and is held under compression within a spring .pocket Abore |55 ina vcoaxially .disposed .operating `shaft |07. The latter is mounted:rotatably by an'encircling ring bearing t 08 :within :an axial .bore |09 `provided therefor .through thetopof the head 30. A split locking ring provides a retaining collar for therop- 1 f. eratingshaft Y|01 at .the base of a serrated head I byvwhich the operating shaft is adapted to be coupled -to '.an .operating lever, shaft or farm under'zthe control ofthe airplane pilot.

.A continuing operational connection between .thefffork head 98 and the operating shaft |07 is `maintained through Vthe medium cf meshing 'spline teeth ||2 and ||3 (Figs. l and 5), in the vvhead and on the stem,.respectively. Packing H4 'about the operating shaft |01 `adords a iluidtight 1 .relationship between the bearing surfaces of'rthe .shaft andthe head 40.

Until hydraulic pressure'iluid is introduced into the unit,'it will .be observed that the compression spring |03 will operate tc hold the fork 95 vchannel IIB and a delivery duct |20'to an laxial passage |2| (Figs. 1 and 7) opening into" the lower end ofthe plunger guide bore 91a which is preferably of somewhat reduced vdiameter and slidably accommodates an axial guide'piston nger |22 at thelower end ofthe plunger 91.

."Thus, vthe hydraulic pressureuid acts upon the .lower end of the piston finger |22 .to drive the *.plunger El .axially outwardlyzagainst the bias'of the compression spring |03 and lifts the rocker fork S5 out oi the locking lrelation in the locking -slot`|00fto clear .the fork .for tilting'of the rocker varm 34. One or vmore pressure relief vent grooves |23.. may be formed in the wall of the plunger vbore Sla, leading from the shoulder alc-ove the reduced diameter portion of the bore to :the rocker plate chamber space at the upper end of Vthe bore. Escape of pressure fluid in either direction along the plug v52 from the channel HS is prevented by appropriate packing or sealing meansas shown. A bore |23a vents bore With the hydraulic pressurefluid acting torelease the rocking fork 35,'the unitisin condition for -selectivelyadmitting the, hydraulic 'pressure fluid to either the working chamber 32 or the working chamber 33 by rotating the operatrection.

4ing shaft |01 to swing the rocking fork 95 to rock or'tilt the rocker plate v85 ineither selective'di- If the rocker plate 85 is actuated to unseat and open the poppet valve 03, hydraulic pressure iiuid is admitted by way of the delivery port 59 to the working chamberj32. The pressure iiuid passes from the pressure `side .of 'the chamber 32 to the diametrically opposite ,supplementary pressure side of the working chamber 33 by way of a cross duct-|24 (Figs. 1 and 10)'.extending transversely through the piston 20. .Likewise, when the poppet valve 04 is opened, hydraulic pressure fluid delivered to the chamber 33 by way of the delivery port 62 goes by Way of a cross duct |25 from the working chamber 33 to the diametrically opposite supplementary pressure side of the working chamber 32. Thus, the hydraulic pressure fluid is applied in Vbal anced relation to the diametrically oppositeportions Vof the working chambers 32 and 33.

At the same .time that hydraulic pressure fluid is admitted to either of the working chambers 32 or 33, the hydraulic iiuid is displaced from the respective non-pressure sides of the working chambers and is conducted through a valvecontrolled displacement or exhaust circuit "to a displacement fluid outlet |21 for return to `a sump or other receptacle for the hydraulic uid. For this purpose, displacement uid ports 128 and |23 (Fig. 8) open adjacent to the upper end of the piston 20 and through the wall of fthe piston and extend into the valve plug 52 from the working chambers32 and 33, respectivelyfat the opposite sides of the vanes 34 fromthe pressure fluid delivery ducts Eiland 62. Each'of the displacement fluid ports l28 and |29 communi- Cates with a respective vertical poppet valve bore |30 companion to the adjacent pressure -rluid controlling poppet valve structure and accommodating a substantially frusto-conical poppet valve |3| in each instance of Videntical const-ruction and adapted to be actuated simultaneously v with the companion pressure fluid controlling lcylindrical guide base -valve normally against its seat |32.

poppet valve 63 or 64.

Each of the displacement iluid poppetvalve |3| is adapted for seating in fluid sealing relation against a valve seat |32 afforded by afslight reduction in the diameter of the upper portion ofthe poppet valve bore |30 immediatelyabove the respective displacement fluid ports |28 .and |29. A reduced diameter coaxial basestem portion |33 extends downwardly from the Apoppet valve to aiicrd a clearance groov'efor space with relation to the mouth of the Ycompanion .displacement port and Aterminates in an venlarged |34 which l'is slidingly bearinged in the upper end of'a sleeve l35;tted into the lower enlarged diameter portion of the bore |33. The lower Vportion of the sleeve V|35 has therein an axial bore |36 fora coiled .compression spring |3'l which bears against .a'lower face |38 on the cylindrical base |34 to bias ".the 'An lupper face |33 on the cylindrical base |34, and anopposing lower face |40 .(Fig. 2) on the valve-member |3| are of substantially the same'area "sofas to afford a balanced or Yequalized fluid pressure condition.

Extending axially upwardly'frcm the poppet valve |3|.'is a reduced diameter head'stem |4| which terminates at its upper end ina Acylindrical head 1.42 which is.slidablyguided-in-the upperA end of `the poppet valve bore 30 :and Lis engagedaxia-lly with anabutment screw VSitaor -92a as the case may be, in the rockerfp1ate-85.

As illustrated in Fig. 2, the displacement poppet valve |3| which is companion to the pressurev fluid controlling poppet valve 63 or 64, as the case may be, is depressed in opposition toits biasing spring |31 simultaneously with the pressure controlling poppet valve. Hence, when hydraulic pressure fluid is admitted into the unit for driving the piston 20, simultaneous displacement relief is afforded for the non-pressure sides of the working chambers -32 and 33. Each of the displacement valve bores |30 has a discharge port |43 (Figs. l and 6) leading therefrom adjacent the upper end into an encircling displacement fluid channel |44 in the surrounding wall of the head 43. Leading from the displacement channel |44 is a discharge port |45 which opens into the outlet |21. Equalized displacement from the working chambers 32 and 33 is effected through the cross-ducts |24 and |25. By having the opposing faces of the displacement poppet valve 13| and the head |42 of substantially the same effective area, fluid pressure thereon is equalized.

By preference, the outlet |21 is provided with I an automatic control valve |41 which may be of the plunger type and urged against a valve seat |48 outwardly of the port |45 by a coiled eX- pansion spring |49. This spring seats at its lower or inner end against the closed bottom end of a downward extension within the head of the bore providing the displacement outlet |21. The upper end of the spring |41 extends upwardly within an aXial pocket provided therefore within the valve plunger |41. The lower end of the valve plunger |41 is slightly enlarged to afford a guide bearing and limit structure slidably disposed within the lower end of the outlet bore |21. The upper reduced end portion of the valve plunger |41 is slidably bearinged in the lower portion of a sleeve |5| formed with a port |52 in registration with the pressure relief port |45. The valve seat |48 is formed by a reduction in diameter of the interior of the sleeve |5| above the. port |52. Precautions against fluid leakage past the valveplunger |41 or the sleeve |5| are taken by the provision of appropriate packing as shown. I

The sleeve |5| is held to an outwardly facing shoulder |53 within the outlet bore |21 below the port |45 by a ring nut |54, and the lower enlarged guide portion of the valve plunger |41 is normally in spaced relation to the inner end of the sleeve so as to afford a space which communicates by way of a duct |54A withthe hydraulic pressure fluid channelv H9. Thus, uponj the introduction of hydraulic pressurel fluid into the unit, the plunger valve 41 is quickly displaced from its seat |48 by action of the pressure fluid on the upper face of thel enlarged plunger base in opposition to the bias of the spring |49 (Fig. 2). This unseated condition is then maintained as long as hydraulic pressure fluid is delivered to the unit so as to have the displacement fluid circuit open under the control of either of the displacement puppet valves 13|. However, once the hydraulic pressure fluid supply is shut olf, automatic plunger valve |41 will immediately close the displacement outlet |21 and thus obviate undesirable back pressure or resurgence of displaced fluid. l

Another function of the plunger control valve |41 is to alford a replenishing means for hydraulic fluid, bfi-passing the poppet valve assembly, to .maintain the working chambers 32 and 33 completely filled when-the unitis working merely as a vibration damper. For this purpose Y lthe plunger valve |41 is provided with an axial borel through the end thereof lopening into the spring pocket |50 therein and affording `a replenishing fluid passage for hydraulic fluid introduced by way of the outlet |21 as a result of back pressure in the displaced fluid or by connecting the outlet with a hydraulic pressure fluid supply source, if desired. 'It is `relatively convenient to maintain the fluid displaced during steering under sufficient head or back-pressure to serve the replenishing purpose. Assuming that replenishment is to be effected by back pressure in the displaced hydraulic fluid, a pair of angular ducts |51 extending through the bottom of the head 40 and through the adjacent portion of the top closure plate member 39 are controlled by respective piston check valves |58 held seated at the-upper ends of appropriate bore enlarge.- ments |59 by means of relatively light coiled expansion springs |60 carried in perforated cages I6 threadedlysecured into the closure plate member 39 at opposite sides of one of the abutments 3| (Fig. 3). Replenishment of theunit is important in order to maintain a filled fluid circuit and avoidthe formation of air pockets within the unit. It may be noted that the ducts |51 are so dispOsed as to :be blocked by the baseof the plunger valve |41 when the pressure iluid supply is live and the valve plunger is inthe open valve position, thus avoiding any short circuiting of displaced fluid during steering operation (Fig. 2). Where fluid replenishment is effected by introducing relatively high pressure hydraulic fluid by way of the outlet v|21 through the outlet control valve plunger 41, it is desirable to use a pressure reducing type of control valve suchas shown in the modification of Fig. 11. Therein ballA valves |58a are urged against their seats by relatively strong respective coiled expansion spring |60a mounted within bottom-perforated .cages |620, threaded into the top vclosure wall member 33 at each side of one of the stationary' vanes 3|, with ball retainer disks |63 holding the ball valves in place underthe influence of the springs. l v

ShouldV the temperature increase and thus cause the hydraulic fluid to expand and cause a rise in the internal pressure, While both the inlet and outlet'ports and passages of the unit are closed, the excess volume of expanded liquid in the` filled system` of the device is adapted to bleed oil slowly past the upper end of the piston 20 through the bearing bore in the upper closure plate 39,which accommodates the piston hub provided by the upwardly projecting portion of the valve plug 52. Thence, the sur-plus liquid leaves by wayof the surrounding fluid channel 5| and A the conducting passage 50 and discharges through date the expansion overflow, the pressure `fluid d inlet 41 is preferably depressurized during nonsteering periods, as by venting to atmosphere.

' `Since itis important for the successful operaducts |68 and |69 lead from the pressure fluid 1.1%l control poppet valve chambers past a lplug-| disposed fast within an axial bore |1| and provided with a pair of annular grooves |12 and |13 registering with the ducts |68 and |69, respec. tively. Bleed ofi ports or ducts |15 and |16 lead olf from the channels |12 and |13, respectively, and communicate with the displacement poppet valve bores or chambers. As the poppet valves |3| arev alternately opened and closed duringsteer-ing, the fluid velocity through the air bleeder ports or ducts, due to pressure dierential between the working chambers 32l and 33, carriesor blows off excess air out therethrough into the discharge or outlet portion of the hydraulicv system.

While-the device is being operated as a steeringl motor, it will, of course, function as a shimmy damper since the vanes 34 will resist any rapid displacement movements in the presence of the hydraulic pressure fluid. Since a' completely lled condition of the hydraulic fluid is maintained in the system and by reason of the complete closing of the system by the poppet valves and various check valves during non-steering periods'or in the event of failure of the hydraulic pressure uid supply, the shimmy dampening function will persist. y

In the closed condition of the unit, blow off displacement of the hydraulic fluid between the working chambers 32 and 33 must be accommodated for elective anti-castering or shimmydamping control. To this end a valve structure is provided which although closing the opposite sides of each of the respective chambersv against a direct transfer of displaced hydraulic fluid duringsteeringoperation, opens a path for metered transfer of displaced hydraulic fluid fromone side of 'each chamber Ato the other side when operating vmerely as a shimmy-damper. Such structure includes a'spool |11 nxedly disposed axially in intersecting relation to the fluid equalizing transverse passages |24 and |25 in the piston 20. A reduced diameterbore |18 leading downwardly from the valve unit plug bore 53 accommodates the spool |11. A lateral flange |19 at the upper end of the spool is xedly secured between the lower end of the plug 52 and the shoulder surrounding the upper endof the bore |18.

To accommodate continuously free equalizing displacement of hydraulic fluid between diametrically opposite portions of the working chambers, by Way of the passages |24 and |25 which it intersects, the-spool |11 is formed with annular grooves |86 andv |8|, respectively, connecting the portions of the intersected' equalizing passages (Figs. 1 and l0). Thus, during steering operations ofthe device, hydraulic pressure fluidor displacement fluid, as the case may be, can flow freely between the diametrically and cooperative opposite portions of the working chambers. Dur- I2 the piston 2G iluid can be displaced from theftwo decreasingly formed high pressure sides of the working chambers into the two respective increas. ingly formed-low pressure sides of the chambers.

To this end, the channeled'spool |11 is providedbetween the displacement fluid passages |26 and' |25. A shoulder 88 at the upper side of the axial orifice |31' affords a valve seat for the plunge valve |82 in its orifice-closing position.

Actuation of the plunger valve |82 is effected by a piston |89 axially reciprocable in a downward extension of the axial ybore |'i| in the-lower Vportieri of the valve plug 52 and connected to the valve plunger 32 by means such as an elongated piston rod or stem |98. A coiled expansion spring |9| working between the piston |39 and a retain-v ing washer |92 seated upon the upper end or the spool |11 normally biases the plunger valve into the inactive or Valve-opening position.

|The upper or pressure face of the piston |89 opposes the lower end of the air blow-ofi" or bleeder plug lle so that the Vlatter in effect provides acylinder head for the piston. Live hydraulic pressure fluid for driving the piston 89 inopposition to the bias of the spring 19| isvv derived from theaxial port i2! and passes through an axial passage ISS in the plugv l'l' to act upon the piston |39 as an incident to the initial introduction of live hydraulic pressure fluid through theinlet, and continuesv toY maintain live uid pressure throughout the steering operation of the device,

1 Vthereby holding the plug valve` |82 in its oriceclosing position until the live pressure fluid supply is discontinued, whereupon the plug valve snaps 'open under the influence of its biasing ing such steering operations, of course, there is a through circuit operating from the pressure fluid inlet 11 and out through the outlet |21, as here'- inbefore described. rTherefore, direct displacement of the hydraulic fluid' from one portion of "55 ofL the hydraulic nuid, controlled displacement between theY respective portie-ns of each of the adjustment by the relative rotary'disposition of Working'chambers 32 and 33 must be provided for. This must be, so that during oscillations of valve |33 in thel form of a cylindrical plug' slidably mounted. Control of hydraulic iluid displacement iow between the axial orifice |81 and the radial slot orifice |94is controlled by the degree ofrotary registration of a chordal-slot orilice i e1 in the plug valve |83 with the slot orifice |94. Full flow registration of an axial bore orilic-e.v |93 in the plug metering valve and the axial orifice |21 aiords a flow path communicating with the slot orifice |61 and cooperating with the slot orifices for fluid metering control. Thus it will be seen, that displacement liow betweenV the high pressure and low pressure sides of the working chambers during ordinary shimrny control operation of the unit issubject to relatively fine the valve spool |11 andthe plug valve |83, Vcontrolling the registration ofthe chordal slot orifices Y |9I1 and |91. Thereby cptimumshimmy dampingaction-ofthe unit is simply and easilyfattainable.

Means are preferably provided for manual adjustment ofthe rotary Valve |83, herein comprising an actuating stem |99 extending in freely rotatable relation through a downward reduced diameter portion 200 of the axial spool bore through the piston shaft 2|. At its lower end, the adjusting stem |99 extends through a retainer and packing gland assembly and is accessible for rotary adjustment from the outer end of piston shaft 2| upon the removal of a closure plug 202.

By having all of the various working spaces on the non-pressure sides or in back of the various hydraulic pressure fluid controlling or responsive valve structures relieved or vented to the discharge or outlet side of the hydraulic circuit of the unit, all pressure resistance to the free functioning of these structures is avoided. As is best seen in Figures l and 2, the return spring working chambers behind the pressure fluid controlling poppet valves 63 and 64 and behind the displacement controlling poppet valves |3|, as well as the space behind the valveoperatingpiston |89 are all interconnected and appropriately vented or placed in communication with the outlet side of the hydraulic circuit through axial passages 203 extending up through the base |34 and base stem |33 of the respective displacement poppet valves |3| and communicating with respective lateral orifices 204 at the outer sides of these poppet valves (Figs. 1 and 7). Intercommunication with the passages 203 is effected through orifices 205 in the poppet valve sleeves 13, connecting with orifices 201 in the wall defining the lower end portion of the piston cylinder bore and the latter connecting with orifices 208 in the poppet valve sleeves |35.

Insofar as the poppet valves is concerned, this also serves the useful purpose of equalizing the pressure at opposite ends of the popnet` valve structure since the working space above the DODDet valves is also in communication with the displacement or outlet side of the hydraulic circuit. To this end the annularr groove |44 in the wall of the head 4 0 surrounding the valve plug 52 at the discharge port |52 communicates with the upper working space or chamber 90 through a. clearance provided for this purpose between the wall of the head 40 and the upper portion of the valveplug 52 above the channel |44 and shown at 209. To implement this eoualization of pressure at the opposite ends of the poppet valves, the opposite end faces thereof. namely, the faces at the top of the head in each instance and the lower end face of the base in each instance, are of substantially equal area.

'While the spring biased form of the poppet valve is preferred, if space limitations prevent the use of the poppet return springs, hydraulically unbalanced poppet valve structures 2| 0 such asshown in the modification of Fig. 9 may be used. In this form of poppet valve, a guide base 2|| of substantially reduced diameter as compared' with the diameter of a valve portion .".|2 is provided so that the inner face of the valve proper, identified at 2|3, presents a substantially greater pressurev area than the opposing upper face of the poppet base so that the internal fluid pressure of the device is effective after the hydraulic pressure supply has been discontinued to drive the valve 2| 2 into closing -relation to its seat. Since the effective pressure areas of the upperside of the valv'e-2|2 and the opposing or inner side of its guide head 2 3a are equal, live pressure fluid introduced therebetween has no driving effect but is neutralized. This leaves the valve always in an unbalanced condition responsive to the internal fluid pressure-against the inner face 2|3. A feature 'of this unbalanced poppet valve structure resides in the sensible response or feel afforded thereby in the cockpit controls so that the piloti's jmade acutely conscious of the action of the steering motor. 'I'his modification may, fof

course, be used both in the pressure fluid conbalance as a result of the completely filled con-- dition of the unit and it functions as a shimmy damper, the various operating components'be'- ing substantially in the relationship shown in Fig. 1. In this condition of the unit, any tendency of the mechanism connected to the end 2| of the piston shaft 20 to rotate the shaft is resisted by action of the pistonvanes 34 on the fluid in the working chambers 32 and 33 of the device; However metered displacement ofthe hydraulic fluid for shock absorbing purposes, that is blow-off displacement between thewo'rking chambers 32 and 33 is accommodated byv Yvalve structure |83. The slight yielding of :the piston shaft 20 oscillatably thus permittedV prevents shimmy from developing'in the associated apparatus such as the airplane wheel controlled by the unit. Furthermore, the structure, in:

cluding the control unit is saved from harmful v`effects of shocks imposed thereon in a manner vfluid is held against traveling further by Vthe normally closed pressure fluid controlling poppet valves 63 and |54. At the same time pressure fluid traveling from the inlet by way of the port H57, the chamber ||1, the passage ||8 and the port |20 enters 'the passage |2| at the center of the valve housing 52 and promptly acts toA shift the blocking plunger |82 to close the passage |81 between the fluid transfer cross ducts |24 and |25; and at the same time drives the plunger 91 axially outwardly to lift the rocker fork Y95 out of the position wherein it locks the operating shaft |01 against rotation relative to the valve housing plug 52.

In the lifted position of the rocker fork its splined coupling with the shaft |01 permits the rocker fork tobe .oscillated selectively by the wshaft |01 to tilt the rocker arm |14v and" thereby the rocker plate 85 for actuating either ofthe fpoppet valves '53,orv64 to open the same simul- Ytaneously with its companion exhaust controlli "pepper, valve IBI. as indicated in Fig. 2` thereby 'in effect to open the fluid circuit from the inlet 41 to the outlet |21 in which the vanes 34 are ilS interposed.- :'I'hus, .as the jpressure fluid acts .upon .theiselected faces .of .-the .vanes vlill asde- .termined by delivery :of the pressure fluid .throught-either of the'ports59 or '62, fluid from theportions -of the Vrespective working cham- Lb'ers 32 and 33 at the OppOSite faces of the vanes 34 is displaced bythe vanes by way of `therespective selected exhaust port .|28 or |29 *,past the associated exhaust controlpoppet valve |3| and thenceport |52 and pastthe automatically -pressure responsive check valve |41 out .through'thefexhaust or outlet'port |27. -Oscil- Ylationof vthepiston can, of course, be effected .to the .limitsbf oscillation defined by the varies .'34. :Such oscillations are transmitted by the :lever or other mechanism attached to the end 2| :of the piston tothe apparatus such as the steering wheel of an airplane with'which the control iunitmay be associated. As long as pressure fluid is--active through the inlet port Vlil, fselective oscillation of the lpiston'ZD can be ef- Lfected at will by turning the shaft |01, and turning of the shaft will continuein the jdesired ndirection'to the .full turning limit or any fraction of theturning distance until the shaft|`| .is :returned to its neutral relation with respect to .the rocker Yplate and the respective pressure .fluid controlling poppet valve returns to closed condition.

' More specifically,if theshaftyl'l 'and the fork 35 are operated clockwise (Fig. 5) to move the vpairof valves B4- |3I'open uid is admitted to the hydraulically connected portions of the vworking chambers 32 `and 33 and is exhausted from ,the opposite Vconnected portions of the chambers 32, v33 lby way 'of port |29 and the :respectively'connected "passages, Y This causes vthe'vanes to'be driven clockwisev to thereby drive :the ro|7ary-pist0n -20 irl-,similar'direction. Upon -cessation of-movement'of-theshaft |01 and the fork 95, the valves 64 and |3| vstill being in the open positions thereof, thevanes 34 continue l`withfa-sliglit follow-jup movement until the plate 85 :returns to neutral position vrelative to the then stationary fork 95 and stem |01 and the valves'f64,' |3| returnto closed position, closing the Aiiuid circuit andbringing thefvanes 34 to a halt. vTurning of-the lshaft v|01 counterclockwise, and Ythus movement 'of the fork 95 counterclockwise, veffects opening-of the companion `v'alves 63, |3| for 'reverse-movement `of the `vanes 34 and the `rotary piston I20, from the movement just described, Withiautornatic stopping of the piston finethe-samemanner when the 'shaft |07 comes toarhalt VrIn the `Vpreferred form of the invention as Ishown-in Figure l,-it will be apparent that since :the valve operating shaftV |01 is at all times fspline coupled with -the poppet lvalve plug 52 `through the 'fork head 98, in the manner here- `inbefore described, the cockpit control may at :all times indicate the precise angular position `.of the, airplane wheel with which -the unit is associated. This is of important Aadvantage in' permitting the pilot to observe at a glance the position of the wheel .and if any adverse. condir.ti-on vexists either for landing or for centering 4during strut-retraction he can hydraulically cor- ;rect thesame. This ...desirable expedient is en .hanced-by the .automaticrealignment or center- ...-16 A return spring ||l3and theguldetprovldedrhythe camsurfaces Il leading to1the.;locking.slot-||l0. This avoids 'any slight out of. phase relationship that may exist in the pilot operated cockpit/.control and the steering motor following anyfsteering activity.

Where `it is desired to have a complete disconnection between the vpilot Ycontrol .and the steering motor at the conclusion of steering factivity, an alternate actuatingstructure such as shown in the modified embodiment of .theinvenftion disclosed in Figure l2 maybe used. 4Inthis form, an actuating shaft '2l-4 is -freelyrotatably vmounted within the'top closureof the head1-52a and is formed vwith inner clutch :teeth .2|5

Yadapted to engage withinlanotchor. notches2 in the upper normally spaced end of a -verti- .cally reciprocable .head v2 8 which' carries a .fork v'95d and is'in other respects 'both:structurally and functionally like vthefor-'lthead 0f vthe pre .ferred form of .the 'invention hereinbefore described. The coiled expansionfspring |03a-normally urges `the head 2|8 Aand the structure thereon downwardly into separated -relationzto the clutch face of the-operating stemv2|4 fand holds the "forka'in its locked position. Upon lthe introduction 'of live pressure fluid -into 'the steering motor, the fork-carrying .head 2|8 fis driven counter the'bias of the spring |03a--into clutching engagementvviththe `clutch face l of .the'shaft 2|4. /If the clutch teeth 2|5 are :out of phase Ywith the "slot 2H, .registration thereof can' be eiected by 'turningof the "actuatingishaft 2 i untilv the" teethl are 'fa'li-gnedfand clutched. In

lthis'form of the Ainventionfof "course,'"the :cockpit .controls will notindicatedthenfangularfmosiltion 'of the `Vairplane Vexcept 'while i'lthe .fmotorfis under the influence of live hydraulic "pressure 'It will, vof Vlcourse, be .understood"thatvarlous ciples kof this invention and itis, theref0re,mot

the `rpurpose to limit'the patent grantedhereon otherwise than4 necessitated byithefscope of Ith'e l`appended claims.

`We'claimas our invention:

l. In combinationin a fdeviceto 'befoperated by hydraulic pressure ui'd, 'means Adefining a 4:duid tight housing, means within saildihousing adapted'to be 'actuated by the 'force of live pressure fluid/means for introducingtlie live'pres- `sure lfluid into 'said housing, means Yaifording an the iiuid and for controlling the displacementfof the vhydraulic fluid from said'means'to be 'actuated to said outlet, nmeans'for selectively actuating said poppet valves,` said actuating means including a rocker plate having La ball arm "extending therefrom and a fork engagingsaid'arm -and selectively `swingable -for rocking the *arm and thereby rocking tlieplate andmeans for .shifting -said forkvinto and fout of a' position wherein the fork is :engageable with `said .rocker .piate-for holding vthe plate inactive.

I2. -In combinationin structure .for controlling a hydraulic fluid-.circut, a ,plurali-ty .of recipro- ,cable -valve members, a rocker plate .for .actuating isaid valve members, .and means for @actuat- `ing `said Yrocker plate .including .a-..meinberf.nor-

n'iallyY locking .the .rocker plate against rocking',

.andresponsive .to live A`hydraulicfliiidpressure .to

17 be moved to non-locking, plate-actuating position.

3. In combination in a combined steering motor and shimmy damper, a cylinder, an oscillatory piston operatively mounted within said cylinder, means for delivering live hydraulic pressure iluid to the cylinder, means for controlling the delivery of the live hydraulic pressure fluid to the piston for alternatively driving the piston rotatably in opposite direction including a plurality of poppet valves and means for actuating said poppet valves, said actuating means including a separable clutch including a live pressure uid actuated clutching member normally assuming a declutched position. 4.- In combination in a hydraulic steering motor and shimmy dampener for airplane landing gear Wheels and the like, a cylinder, an oscillatory piston in said cylinder and having a shaft extending from one end of the cylinder, means for delivering live hydraulic pressure lluid to the opposite end of the cylinder, means carried by the opposite end of the piston from said shaft for controlling the delivery of the live pressure fluid for actuating the piston and including a plurality of poppet valves and mechanism for actuating said poppet valves selectively, an outlet leading from the cylinder including a control valve normally closing the outlet but responsive to live pressure fluid to open the outlet, said outlet controlling valve having a replenishing fluid 'passage therethrough, and means at all times affording restricted communication for make-up fluid between said outlet and the interior of the cylinder by Way of said passage.

5. In combination in a combined steering motor and shimmy damper unit a cylinder structure, a piston structure operative Within said cylinder structure, means for delivering hydraulic pressure fluid to the cylinder structure for actuating the piston structure for steering purposes, means affording an outlet for displaced hydraulic iluid during steering operation, valve means for controlling the inlet and outlet means and adapted to close the same during non-steering intervals for maintaining a fluid-filled condition in the unit for shimmy dampening purposes, and means by-passing the outlet valve means in the closed condition of said valve means for replenishing the unit through said outlet 'means to compensate for shimmy dampening fluid losses.

6. In combination in a combined hydraulic steering motor and shimmy dampener of* the character described, a cylinder structure, a piston operable within said cylinder structure, means for delivering hydraulic pressure fluid to the cylinder structure for actuating the piston, means providing an outlet for spent pressure iluid, and control valve structure for controlling said iluid delivery and outlet means for maintaining the cylinder illled with the hydraulic iluid upon discontinuance of the hydraulic pressure iluid supply so that the unit will continue functioning as a shimmy dampener, and means operative during the delivery of the pressure fluid supply for venting the unit of air.

'7. In combination in a hydraulic steering motor and shimmy dampener unit, a cylinder structure, a piston structure operable in said cylinder structure, means for supplying hydraulic pressure fluid for actuating the piston structure for steering purposes, means providing an outlet for spent pres-sure fluid yduring steering, and valve mechanism for controlling both the fluid delivery and outlet means to aiord a closed fluid-filled condition within the unit during non-steering intervals for operation of the piston for shimmy dampening, and means affording pressure release through said pressure fluid delivery means upon thermal expansion of the hydraulic fluid Within the unit while the unit is serving merely as a shimmy dampener.

8. In combination in a combined hydraulic steering motor and shimmy dampener unit, a cylinder structure, a vaned piston operable in said cylinder structure and affording working chambers therein, means for supplying hydraulic pressure iluid to the working chambers for actuating the piston oscillatably for steering purposes, means affording an outlet for spent pressure fluid, valve mechanism for controlling the fluid delivery and the outlet means and operable during nonsteering intervals to close the `unit to afford a hydraulic lluid filled shimmy dampener, said piston having displacement passages therethrough for displacement of fluid Within the Working chambers during shimmy dampening, and live pressure iluid responsive valve means for closing said passages against said shimmy displacement of uid during operation of the unit as a steering motor.

9. In combination in a hydraulic steering motor and shimmy dampener unit, a cylinder structure, closures for the opposite ends of the cylinder structure, diametrically opposite abutment vanes Within the cylinder structure, an oscillatory vaned piston Within the cylinder structure and cooperating with said abutment vanes toprovide Working chambers, means for supplying live pressure fluid to said chambers for actuating the piston for steering purposes, valve means for controlling said pressure iluid delivery means to maintain the Working 'cylinders lled with hydraulic fluid during non-steering intervals when the delivery of hydraulic pressure fluid is discontinued, cross passages in said piston for balanced delivery of hydraulic pressure iluid during steering operations, said piston having orifices therein v affording communication between said passages for hydraulic fluid displacement during shimmy dampening operations of the unit. pressure fluid responsive valve means for closing said orices during steering motor operations of the unit and adapted to open automatically upon discontinuance of the pressure uid supply, and metering Valve structure for controlling resistance to displacement ilow through said orifices.

10. In combination in a hydraulic steering motor and shimmy dampener unit, a cylinder structure, an oscillatory piston Within said cylinder structure, a shaft on said piston extending Ifrom one end of the cylinder structure, a closure member disposed at one end of the cylinder structure through which the shaft extends, a relatively thin closure member for the opposite end of the cylinder structure, means for securing said thin closure member in place, means for delivering live hydraulic pressure iluid through said securing means to said cylinder for actuating said piston, and means for substantially equalizingethe live hydraulic iluid pressure on opposite sides of said thin closure member.

11. In combination in a hydraulic steering motor and shimmy dampener unit, a cylinder structure, a piston structure operable in said cylinder structure, one end of said piston structure having a shaft extending from one end of the cylinder structure, the opposite end of tne'piston having .a plug structure mounted therein and support- .ing a control valve structure, means for supplying hydraulic pressure iluid through said control valve structure to the cylinder structure for operating the piston, and means for controlling said valve structure exteriorly of the unit cooperatively related to said plug structure, said piston structure having displacement flow controlling valve means therein, said plug-carried valve structure being responsive to live hydraulic pressure fluid to act with said displacement valve means for controlling fluid displacement While the unit is subjected to live uid pressure.

12. In 'combination in a hydraulic pressure iluid controlled steering motor, a housing provid- `ing a cylinder, an oscillatory vaned piston operable in said cylinder, said piston including a control valve-carrying extension at one end thereof and oscillatable with the piston, means surrounding said extension and including pressure lluid supply and exhaust fluid passages, said eXtension and said piston having intercommunicating passages between said supply and exhaust passages and the interior of the cylinder for operation of the piston, respective valves carried by said extension for controlling flow of uid Athrough said intercommunicating passages, a

valve controlling rocker plate pivotally carried by the outer end portion of said extension and thereby oscillatable with the extension, a rocker plate actuating member carried by said extension and mounted for oscillation relative to the extension, and means for oscillatably actuating said rocker plate actuating member relative to said extension for rocking the rocker plate to actuate said control valves.

13. In combination in a combined hydraulic steering motor and shimmy dampener unit, a cylinder structure, a vaned piston operable in said cylinder structure and affording working chambers therein, means for supplying hydraulic pressure fluid to the Working chambers for actuating the piston oscillatably for steering purposes, means affording an outlet for spent pressure uid, valve mechanism for controlling the uid delivery and the outlet means and operable :during non-steering intervals to substantially close the unit to aord a hydraulic uid filled shimmy dampener, means for operating said valve mechanism including spring means for nor- .mally biasing the same into inactive condition and a iluid responsive Aplunger operable to overcome the spring means, said `piston having displacement passages therethrough for displacement of uid within the rworking chambers dur- .ing shimmy dampening, and live pressure-fluidresponsive'valve means for closing said passages against-said shimmy displacement of fluid during `operation of the unit vas a steering motor, said Vfluid-responsive valve means including a pressure-sensitive plunger operatively aligned with vsaid first mentioned plunger, said fluid supplying means having a by-pass passage therefrom for delivering live pressure fluid for actuating said plungers simultaneously.

14. In combination in a combined hydraulic steering motor and shimmy damper unit, a cylinder structure, a vaned piston operable in said cylinder structure and affording working chambers therein, means for supplying hydraulic pressure uid to the Working chambers for actuating the piston oscillatably for steering purposes, means affording an outlet for 'spent pressure fluid, valve mechanism for controlling lthe fluid delivery and the outlet means and operable during vnon-steering intervals to close the unit to aiord a hydraulic fluid filled shimmy damper, means for operating said valve mechanism normally spring biased into non-operating position and including a pressure-sensitive plunger, 'and means providing a live pressure fluid by-pass from said pressure fluid supplying means to supply live'pressure fluid for actuating said plunger.

15. In combination ina combined hydraulic steering motor and shimmy damper unit, acylinder structure, a vaned piston operable in said cylinder structure and affording Working chambers therein, means for supplying hydraulic pressure fluid to the working chambers for actuating the piston oscillatably for steering purposes, means affording an outlet for spent pressure fluid, respective poppet valves carried by said piston for controlling the iiuid delivery means and the outlet means, respectively, and operable during non-steering intervals to close the unit to afford ka hydraulic uid iilled shimmy damper, each of said poppet valves having a piston-type base and said piston having cylindrical guides in which said bases are reciprocably slidable, said piston having displacement passages therethrough for displacement of fluid Within the Working chambers during shimmy dampening, and a valve for .closing said passages against said shimmy displacement iof fluid during operation of the unit as a steering motor, said valvev having a stem extending therefrom and alive pressureuid-responsive piston Vhead on said stem, said vaned piston .having cylindrical guides for said last 'mentioned valve and said piston head, `the space behind said base of the poppet valve controlling thefluid delivery means being ported for pressure .relief to the space between the displacement passage closing valve and the piston head thereon and said last mentioned space being vented to the space behind the piston base of the poppet valve controlling said outlet means, said base lof the poppet valve controlling the outlet means being vented for pressure relief to said outlet means.

16. In combination in a hydraulic steering motor unit of the character described, a casing dening a cylinder and having closures at the opposite ends thereof, Yan loscillatory vaned piston in saidcylinder land vhaving a shaft extending through one of the end closures, means in the opposite end closure deningrpressure uid inlet passage and separate fluid outlet passage, a separate plug vbody carried-by the opposite .end .portion of the piston and secured for oscillation with the piston, said plug bodyextending beyond said opposite-end of the piston, said opposite end closure providing a sliding .bearing `for the projecting portion of said plug body, said plug body having fluid communication passageways therethrough .to provide communication between said inlet and outlet means and .the 'interior of the cylinder, valves carried by said plug body for controlling said Dassagevvayameans for operating said valves carried by the outer end portion of said plug body, and means for actuating said valve operating means including a stem projecting from s aid opposite vend closure.

HARRY -L. CHISHOLMI, JR.

GEORGE lFARRELL. BERNARD E. OCONNOR.

(References on 'following page) l REFERENCES CITED UNITED STATES PATENTS Number Name Date Bergesen May 22, 1906 Ogle NoV. 11, 1913 Ross Mar. 11, 1924 Craig Sept. 4, 1928 Banning Apr. 23, 1929 Pppy June 14, 1932 Tucker Sept. 6, 1932 Vickers Feb. 18, 1936 Number Number Name Date Colman June 24, 1941 Herman Mar. 10, 1942 Mercier Aug. 18, 1942 Thacker Dec. 15, 1942 Ray Dec. 12, 1944 Chisholm Apr. 3, 1945 Orshansky May 2, 1945 Chisholm Aug. 28, 1945 FOREIGN PATENTS Country Date Great Britain June 2, 1932 

